High performance sub-system design and assembly

ABSTRACT

A multiple integrated circuit chip structure provides interchip communication between integrated circuit chips of the structure with no ESD protection circuits and no input/output circuitry. The interchip communication is between internal circuits of the integrated circuit chips. The multiple integrated circuit chip structure has an interchip interface circuit to selectively connect internal circuits of the integrated circuits to test interface circuits having ESD protection circuits and input/output circuitry designed to communicate with external test systems during test and burn-in procedures. The multiple interconnected integrated circuit chip structure has a first integrated circuit chip mounted to one or more second integrated circuit chips to physically and electrically connect the integrated circuit chips to one another. The first integrated circuit chips have interchip interface circuits connected each other to selectively communicate between internal circuits of the each other integrated circuit chips or test interface circuits connected to the internal circuits of each integrated circuit chip to provide stimulus and response to said internal circuits during testing procedures. A mode selector receives a signal external to the chip to determine whether the communication is to be with one of the other connected integrated circuit chips or in single chip mode, such as with the test interface circuits. ESD protection is added to the mode selector circuitry.

This application is a Continuation-in-Part of Ser. No. 09/729,152, filedon Dec. 4, 2000, now U.S. Pat. No. 6,303,996 which is a Divisionalapplication of Ser. No. 09/258,911 filed on Mar. 1, 1999, now issued asU.S. Pat. No. 6,180,426.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to structures and methods of assembly ofintegrated circuit chips into interconnected multiple chip modules. Moreparticularly, this invention relates to multiple chip structuresconnected physically and electrically.

2. Description of the Related Art

The manufacture of embedded Dynamic Random Access Memory (DRAM) requiresthat process parameters that enhance the performance of the logic or theDRAM, if separately formed on semiconductor chips, be compromised whenDRAM is embedded into an array of logic gates on the same semiconductorchip. This compromise has limited the application of embedded DRAM. Ifthere is no compromise in the process parameters to enhance theperformance of logic or the embedded DRAM, the manufacturing processbecomes very complicated and costly. Moreover, because of the structureof the embedded DRAM and the logic, burn-in of the embedded DRAM is notpossible and embedding of DRAM with logic is not a reliable designsolution.

A multiple chip module structure is a viable alternative to embeddedDRAM. With multiple chips connected in intimate contact, the processparameters that maximize the performance of the DRAM chip and the logicgates can be applied during manufacture. Refer to FIG. 1 for adescription of a “chip-on-chip” structure 100. Such a “chip-on-chip”structure is described in U.S. Pat. No. 5,534,465 (Frye et al.). A firstintegrated circuit chip 105 is attached physically and electrically to asecond integrated circuit chip 110 by means of an area array of solderbumps 115. The process of forming an area array of solder bumps 115 iswell known in the art and is discussed in Frye et al. 465. The secondchip 110 is then secured physically to a substrate 120. Electricalconnections 125 between the second integrated circuit chip 110 andexternal circuitry (not shown) are created as either wire bonds or tapeautomated bonds. The module further has a ball grid array 130 to securethe structure to a next level of packaging containing the externalcircuitry. Generally, an encasing material 135 is placed over the“chip-on-chip” structure 100 to provide environmental protection for the“chip-on-chip” 100.

U.S. Pat. No. 5,481,205 (Frye et al.) teaches a structure for makingtemporary connections to integrated circuit chips having “solder bumps”or connection structures such as ball grid arrays. The temporaryconnections allow temporary contacting of the integrated circuit chipduring testing of the integrated circuit chip.

The handling of wafers from which the integrated circuit chips areformed and the handling of the integrated circuit chips themselvescauses the integrated circuit chips to be subjected to electrostaticdischarge (ESD) voltages. Even though connections between the firstintegrated circuit chip 105 and the second integrated circuit chip 110are relatively short and under normal operation would not be subjectedto ESD voltages, ESD protection circuitry is required to be formedwithin the interchip interface circuit to provide protection ornecessary driving capacity for the first integrated circuit chip 105 andthe second integrated circuit chip 110 during burn-in and othermanufacturing monitoring processes.

U.S. Pat. No. 5,731,945 and U.S. Pat. No. 5,807,791 (Bertin et al.)teach a method for fabricating programmable ESD protection circuits formultichip semiconductor structures. The interchip interface circuit oneach integrated circuit chip is formed with an ESD protection circuitand a switch to selectively connect the ESD protection circuit to aninput/output pad. This allows multiple identical chips to beinterconnected and redundant ESD protection removed.

The circuits at the periphery of integrated circuit chip s generally arespecialized to meet the requirements of standardized specifications.These include relatively high current and voltage drivers and receiversfor communicating on relatively long transmission line media.Alternately, as shown in U.S. Pat. No. 5,461,333 (Condon et al.) theinterface may be differential to allow lower voltages on thetransmission line media. This requires two input/output pads fortransfer of signals.

U.S. Pat. No. 5,818,748 (Bertin et al.) illustrates a separation of chipfunction onto separate integrated circuits chips. This allows theoptimization of the circuits. In this case, EEPROM is on one integratedcircuits chip and drivers and decoders are on another. The chips areplaced face to face and secured with force responsive self-interlockingmicro-connectors.

FIGS. 2a and 2 b show multiple “chip-on-chip” structures 100 constructedon a wafer. Not shown is the forming of the first integrated circuitchip on a silicon wafer. The first integrated circuit chip is tested onthe wafer and nonfunctioning chips are identified. The wafer isseparated into the individual chips. The functioning first integratedcircuit chips 105 then are “flip-chip” mounted on the second integratedcircuit chip 110 on the wafer 200. The wafer 200 is then separated intothe “chip-on-chip” structures 100. The “chip-on-chip” structures 100 arethen mounted on the modules as above described.

SUMMARY OF THE INVENTION

An object of this invention is to provide a multiple integrated circuitchip structure where the interchip communication between integratedcircuit chips of the structure have no ESD protection circuits and noinput/output circuitry. The interchip communication is between internalcircuits with a minimal electrical load.

Another object of this invention is to provide a circuit to selectivelyconnect internal circuits of the integrated circuits to test interfacecircuits having ESD protection circuits and input/output circuitrydesigned to communicate with test systems during assembly and test.

A further object of the invention is to provide a circuit to selectivelyconnect internal circuits of the integrated circuits to one of twopaths, either for single chip mode operation or for multi-chip modeoperation.

To accomplish these and other objects, a multiple interconnectedintegrated circuit chip structure has a first integrated circuit chipphysically and electrically connected to one or more second integratedcircuit chips. The integrated circuit chips may be connected to oneanother by means of an area array of solder bumps. The first integratedcircuit chip has interchip interface circuits connected to the one ormore second integrated circuit chips to communicate between internalcircuits of the first and second integrated circuit chips and testcircuits. The test circuits are connected to the internal circuits ofthe first integrated circuit chip to provide stimulus and response tothe internal circuits during testing procedures. Additionally, the firstintegrated circuit chip can be set to be operated in single chip mode,if desired.

The second integrated circuit chips have input/output interfacecircuitry to communicate with external circuitry connected to the secondintegrated circuit chips and to protect the second integrated circuitchips from electrostatic discharge voltages. Further, the secondintegrated circuit chips have interchip interface circuits connected tothe first integrated circuit chip and to each other to communicatebetween the internal circuits of the chips and with test circuits. Thetest circuits are connected to the internal circuits of the secondintegrated circuit chips to provide stimulus to and response from theinternal circuits during testing and burn-in procedures.

The interchip interface circuitry has an internal interface circuit fortransferring electrical signals between the internal circuits of oneintegrated circuit chip to another integrated circuit chip. Theinterchip interface circuitry further has a mode select switch toselectively connect between the internal circuits of one integratedcircuit chip and another integrated circuit chip or to operate in singlechip mode, including stand-alone operation or connection to testinterface circuits. The mode select signal to the mode switch isexternal to the chip. The signal may come from another of the integratedcircuit chips, from the substrate, or from a test interface, or otherexternal source. The mode switch has three terminals and a controlterminal. The first terminal is connected to an output of the internalinterface circuit, a second terminal connected to the internalcircuitry, and the third terminal connected to an input/outputinterface. A mode selector is connected to the control terminal. Thestate of the mode selector determines the connection between the firstterminal and thus the output of the internal interface circuit, thesecond terminal and thus the internal circuitry, and the third terminaland thus the test interface or other interface. During multi-chip modeoperation, the first terminal is connected to the second terminal suchthat the internal circuits of two integrated circuits are connectedthrough their respective internal interfaces. During single chip modeoperations, the internal circuits are connected to an input/outputinterface. For example, during test and burn-in, the input/outputinterface may connect to external testing circuitry.

The first integrated circuit chip could be fabricated using a first typeof semiconductor process and the second integrated circuit chip would befabricated with a second type of semiconductor process that is notcompatible with the first type of semiconductor process, and so on. Asan example, the first integrated circuit chip could be an array ofmemory cells and the second integrated circuit chip would containelectronic circuitry formed with a process not compatible with a processof the array of memory cells. Alternatively, the second integratedcircuit chip is an array of memory cells and the first integratedcircuit chip contains electronic circuitry formed with a process notcompatible with a process of the array of memory cells. Other integratedcircuit chips could be fabricated in other ways. Fabricating the firstintegrated circuit chip using its optimum semiconductor process,fabricating the second integrated circuit chip using its optimumsemiconductor process, and then joining the first and second integratedcircuit chips by this invention creates a multiple chip integratedcircuit structure having maximum performance with minimum cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a “chip-on-chip” structure of theprior art.

FIGS. 2a and 2 b are respectively top view and a cross-sectional view ofa “chip-on-chip” structure formed on a semiconductor wafer of the priorart.

FIG. 3 is a cross-sectional view of a “chip-on-chip” structure,schematically the circuitry contained on each chip of the chip-on-chipstructure of this invention.

FIGS. 4a-d are schematics of the interchip interface circuits of thisinvention.

FIGS. 5a and 5 b are schematic drawings of an embodiment of theinterchip interface of this invention.

FIGS. 5c and 5 d are schematic drawings of an alternative embodiment ofthe interchip interface of this invention.

FIGS. 6a and 6 b are top surface views of the first and secondintegrated circuit chips of FIG. 3 showing test pads and interchipinput/output pads of this invention.

FIGS. 7a through 7 d are examples of multiple chip modules that could bemade using the process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The process and structure of the present invention can be extended toany kind of format of multi-chip module. For example, two or a few chips72 and 74 may be mounted on the same side of the ball grid arraysubstrate 76 as shown in FIG. 7a. The ball grid array 76 is shownattached to the substrate 78. The substrate can be laminated printedcircuit boards, or ceramic, glass, aluminum, copper, or any kind ofsubstrates. FIGS. 7b through 7 d illustrate other examples of multiplechip configurations. In all of these examples, more than the two chipsshown can be connected together. The following figures illustrate a“chip-on-chip” structure. It will be understood by those skilled in theart that the present invention should not be limited to any of theexamples shown, but can be extended and applied to any kind of format ofmultiple chip module.

A “chip-on-chip” structure 300 is shown in FIG. 3. A first integratedcircuit chip 305 is attached to a second integrated circuit chip 310 bymeans of an area array of solder bumps 315, for example, as describedabove. The second integrated circuit chip 310 is secured physically tothe module 320. The electrical connections 325 are either wire bonds orTAB bonds. The module 320 has a ball grid array 330 to attach the“chip-on-chip” structure within the module to a next level of electronicpackage. It will be understood that more than two chips may be connectedin this way and that the chips may be connected on the same side of theball grid array 330 or on opposite sides.

The first integrated circuit chip 305 has internal circuits 335, whichare the functional electronic components of the first integrated circuitchip 305. The internal circuits 335 may be DRAM, logic, or otherintegrated circuits. Likewise, the second integrated circuit chip 310has the internal circuits 365. The internal circuits 365 are thefunctional electronic components of the second integrated circuit chips310. These internal circuits also may be DRAM, logic, or otherintegrated circuits. To transfer signals between the internal circuits335 of the first integrated circuit chip 305 and the internal circuits365 of the second chip 310 or to an external test system, the internalcircuits 335 are connected to the interchip interface circuits 340. Theinterchip interface circuits 340 are connected through the input/outputpads 345 to the area array of solder bumps 315 and thus to the secondchip 310. This connection is functional during multi-chip modeoperation, when the first integrated circuit chip 305 is mounted to thesecond integrated circuit chip 310. These input/output pads 345 have noelectrostatic discharge (ESD) circuits or driving circuits. Theinput/output pads 345 are used in multi-chip modules to bond to otherchips, substrates, or other interconnection media.

For single chip operation mode, the interchip interface circuit 340 isbonded to the input/output pads 355 having ESD and driving circuits forstand-alone performance. The bonding may be by wire bonding, solderbumping, or any other interconnection means to a substrate or any othersecond level chip carriers. The input/output pads 355 connect to theinput/output or test interface 350.

The mode select 390 for the first integrated circuit chip 305 isaccomplished by placing an appropriate logic level on the mode selectinput/output pads 391 and 392. When the first integrated circuit chip305 is operating in single-chip mode, the mode select input/output pad391 is brought to a first logic level (0) for stand-alone performance.The system designer could connect the mode selector to an externalsource (such as from a printed circuit board) which can provide logiclevel (0).

When the first integrated circuit chip 305 is mounted to the secondintegrated circuit chip 310 for multi-chip operation, the mode selectline 390 is brought to a second logic level (1) through the mode selectinput/output pad 392. The second logic level (1) is a voltage equal tothe power supply voltage source V_(DD) and is achieved by connecting themode select input output pad 392 to the mode select input/output pad 393on the second integrated circuit chip 310 through the solder ball 394.The mode select input/output pad 393 is connected directly to the powersupply voltage source V_(DD) to achieve the second logic level (1). Whenthe mode select line 390 is at the second logic level (1), the interchipinterface 340 transfers signals of the internal circuits 335 to theinput/output pads 345 to the second integrated circuit chip 310 asdescribed above.

It should be emphasized that the mode select signal is external to thechip. During single-chip mode, such as during testing and burn-in, themode select signal is from the test probe and the burn-in socket,respectively. These signals to the mode select input/output pad bringthe pad to the first logic level (0), as described above. Afterassembly, when the circuit is in operation, the mode select signal cancome from other chips or from the substrate directly to cause signals ofthe internal circuits to transfer to output pads for one of the otherchips, for example. Alternatively, single-chip operation can still beselected after assembly by setting the mode selector to single chipmode. The advantage of this concept is to extend the application forchips having this inventive design to serve multiple purposes. Thisenhances the commercial value and cost effectiveness of the design.

The internal circuits 365 of the second integrated circuit chip 310likewise are connected to the interchip interface circuits 360. Theinterchip interface circuits 360 are connected to the input/output pads370 and thus to the first integrated circuit chip 310 through the areaarray of solder bumps 315. The interchip interface circuits 360 areconnected to the I/O or test interface circuits 375.

The internal circuits 365 of the second integrated circuit chip 310 areconnected to the input/output interface 385. The input/output interfaceis connected to the input/output pad 395, which is connected to themodule 320 through the bondwire 325. The input/output interface providesthe circuitry to transfer signals between the internal circuits 365 andthe external circuits attached through the next packaging level to theball grid array 330 and thus to the wirebond 325.

The second integrated circuit chip 310 is tested prior to separation ofa wafer containing the second integrated circuit chip 310, by bringingtest probes or needles of the test system in contact with theinput/output pads 395 and the test input/output pads 377. Subsequent todicing of the wafer into individual second integrated circuit chips 310,the individual second integrated circuit chips 310 are mounted in aburn-in apparatus. The burn-in apparatus again is brought in contactwith the input/output pads 395 and the test input/output pads 377 toprovide stressing signals to the circuits of the second integratedcircuit chip 310. Then, when the first integrated circuit chip 305 ismounted to the second integrated circuit chip 310, operation of thewhole “chip-on-chip” assembly 300 is verified by attaching testingprobes or contacts to the ball grid array 330. Signals from the testingprobes are transferred between the circuits of the whole “chip-on-chip”assembly 300 through the bond wires 325 to the input/output pads 395.

The mode select 380 for the second integrated circuit chip 310 isaccomplished by placing an appropriate logic level on the mode selectinput/output pads 381 and 382. When the second integrated circuit chip310 is in contact with a test system during wafer testing or die testingduring burn-in, the mode select input/output pad 381 is brought to afirst logic level (0) to cause the interchip interface circuit 360 totransfer signals between the internal circuits 365 and the I/O or testinterface 375. The test signals are then transferred between the I/O ortest interface 375 and the test input/output pad 377 as described above.Again, it is noted that the mode select signal comes from outside thechip; from the test probe or burn-in socket, for example, in the testingphase.

When the first integrated circuit chip 305 is mounted to the secondintegrated circuit chip 310 and multi-chip mode is desired, the modeselect line 380 is brought to a second logic level (1) through the modeselect input/output pad 382. The second logic level (1) is achieved byconnecting the mode select input output pad 382 to the mode selectinput/output pad 383 on the second integrated circuit chip 310 throughthe solder ball 384. The mode select input/output pad 383 is connecteddirectly to the power supply voltage source V_(DD) to achieve the secondlogic level (1). When the mode select line 380 is at the second logiclevel (1), the interchip interface 360 transfers signals of the internalcircuits 365 to the input/output pads 370 to the first integratedcircuit chip 305 as described above. The mode select signal comes fromthe substrate or from the other chips during operation of the circuit.

The input/output interface circuit 385 has an input/output buffer 389connected to the internal circuits 365. The input/output buffer 389 iseither a driver or receiver necessary to translate the signal levels ofthe internal circuits 365 to the signal levels of the external circuitsand the signal levels of the external circuits to the signal levels ofthe internal circuit 365. The input/output buffer is connected to theinput/output pad 395 and to the ESD protection circuit 387. The ESDprotection circuit 387 clamps excess ESD voltages to prevent damage tothe input/output buffer 389 and the internal circuits 365 from ESDvoltages brought in contact with the input/output pad 395 from theexternal environment.

FIGS. 4a through 4 d illustrate a key feature of the present invention:to provide two alternative input/output paths. One I/O path has anelectrostatic discharge (ESD) protection circuit and a driving circuitwhile the other path has no extra loading. One of the two paths isselected by a mode switch.

FIGS. 4a and 4 d show schematically the connections of the interchipinterface 340 and the I/O or test interface 350 of the first integratedcircuit chip 305 of FIG. 3. FIG. 4a illustrates a path of a signaloriginated within the internal circuits 400 of the first integratedcircuit chip and FIG. 4d illustrates a path of a signal originatedexternally and received by the internal circuits 462 of the firstintegrated circuit chip.

Referring now to FIG. 4a, the interchip interface 340 is comprised of amode switch 402 and a mode selector 404. The signal 400 originating fromthe internal circuit of the first integrated circuit chip is connectedto a first terminal of the mode switch 402. The second terminal of themode switch 402 is connected directly to an input/output pad of thefirst integrated circuit chip and thus to the internal circuits of thesecond integrated circuit chip or other external circuits, as describedabove. The third terminal of the mode switch 402 is connected to the I/Oor test interface 350. The I/O or test interface circuit 350 is composedof a driver circuit 410 connected to input/output pad 412 and then to atest probe or burn-in socket or other external probe and to the ESDprotection circuit 414. The ESD protection circuit 414 operates as theESD protection circuit 387 of FIG. 3 and clamps excessive ESD voltage toprotect the I/O or test interface circuit 350 from damage duringhandling of the wafer containing the first integrated circuit chip formanufacturing, assembly, testing, and stand-alone operation.

The control terminal of the mode switch 402 is connected to a modeselector 404 to control the function of the interchip interface 340. Thesignal to the mode selector comes form the substrate, the secondintegrated circuit chip, test probe, burn-in socket, or other externalsource. When the mode selector 404 is at a first logic state (0), theinternal circuits 400 of the first integrated circuit chip are connectedto the I/O or test interface circuit 350. When the mode selector 404 isat a second logic state (1), the internal circuits 400 of the firstintegrated circuit chip are connected to the input/output 408 and thusto the internal circuits of the second integrated circuit chip. The modeselector 404 is set to the first state during the testing procedures ofthe wafer containing the first integrated circuit chip or duringstand-alone operation. Conversely, when the mode selector 404 is set tothe second logic state during the multi-chip mode operation of the“chip-on-chip” structure.

Referring to FIG. 4d, the signals originating in the internal circuitsof the second integrated circuit chip or other external source aretransferred to the chip pad 454 of the first integrated circuit. Thechip pad 454 is connected to the first terminal of the mode switch 456.The I/O or test interface circuit 350 is connected to the secondterminal of the mode switch 456. The third terminal of the mode switch456 is connected to the internal circuits 462 of the first integratedcircuit chip. The control terminal of the mode switch 456 is connectedto the mode selector 458 to control the function of the interchipinterface 340. The signal to the mode switch comes from the substrate,the second integrated circuit chip, a test probe or burn-in socket, orother external source. If the control terminal of the mode switch 458 isat the first logic state (0), the I/O or test interface circuit 350 isconnected to the internal circuit of the first integrated circuit chip.Conversely, if the control terminal of the mode switch 458 is at thesecond logic state (1), the chip pad 454 of the first integrated circuitchip and thus internal circuits of the second integrated circuit chipare connected to the internal circuits of the first integrated circuitchip.

As described above, the mode selector 458 is set to the first logicstate during the testing procedures of the wafer containing the firstintegrated circuit chip or during stand-alone operation and the modeselector 458 is set to the second logic state during multi-chipoperation of the “chip-on-chip” structure.

FIGS. 4b and 4 c show schematically the connections of the interchipinterface 360 and the I/O or I/O or test interface 375 of the secondintegrated circuit chip 310 of FIG. 3. FIG. 4c illustrates a path of asignal originated within the internal circuits 430 of the secondintegrated circuit chip and FIG. 4b illustrates a path of a signaloriginated externally and received by the internal circuits 432 of thesecond integrated circuit chip.

FIG. 4b shows the instance where the signals originate on the firstintegrated circuit chip or other external source and are transferredthrough to the input/output pad 422 of the second integrated circuitchip. The input/output pad 422 is connected to the first terminal of themode switch 424. The I/O or test interface circuit 375 is connected tothe second terminal of the mode switch 424. The third terminal of themode switch 424 is connected to the internal circuits 430 of the secondintegrated circuit chip. The control terminal of the mode switch 424 isconnected to the mode selector 426, which operates as described above.The signal to the mode selector comes from the substrate, the firstintegrated circuit chip, a test probe or burn-in socket, or othersource. If the mode selector is at the first logic state (0), the testsignals from an external test system or other I/O source are transferredthrough the I/O or test interface 375 to the internal circuits 430 ofthe second integrated circuit chip. Alternatively, if the mode selector426 is at the second logic state (1), the signals from the internalcircuit of the first integrated circuit chip are connected through theinput/output pad 422 to the internal circuits 430 of the secondintegrated circuit chip. Again, as described above, the mode selector426 is set to the first logic state during testing procedures or singlechip mode operation and is set to the second logic state duringmulti-chip mode operation.

The I/O or test interface is similar to that described in FIG. 4d. Thetest or I/O signals originating in an external test system, such as froma test probe or burn-in socket or other source, are applied to a test orinput/output pad 416. The test or input/output pad 416 is connected to areceiver 420 and ESD protection circuit 418. The receiver 420 translatesthe test signals to signal levels acceptable by the internal circuits430 of the second integrated circuit chip. The ESD protection circuit418 clamps ESD voltages applied to the I/O or test pad 416 to preventdamage to the second integrated circuit chip.

FIG. 4c shows the instance where the signals originate in the internalcircuits 432 of the second integrated circuit chip and are transferredthrough chip pad 438 to the first integrated circuit chip. The firstterminal of the mode switch 436 receives the signals from the internalcircuits 432 of the second integrated circuit chip. The second terminalof the mode switch 436 is connected to the chip pad 438. The thirdterminal is connected to the I/O or test interface 375. The controlterminal is connected to the mode selector 434.

As described above, the mode selector 434, having an input from thefirst integrated circuit chip, the substrate, a test probe, or burn-insocket or other external source, determines the connection of theinternal circuits 432 to either the chip pad 438 or the I/O or testinterface circuit 375. If the mode selector 434 is set to the firstlogic state (0), the internal circuits 432 are connected to the I/O ortest interface circuit 375, to a test probe or other external source forsingle-chip mode. Alternatively, if the mode selector 434 is at thesecond logic state, the internal circuits 432 are connected through thechip pad 438 to the internal circuits of the first integrated circuitchip or other external location for multi-chip mode.

The mode selector 434 is set to the first logic state during single chipoperation, including testing procedures and to the second logic stateduring multi-chip system operation.

FIGS. 5a and 5 b illustrate the structure of a sample embodiment of themode switch and the mode selector shown in FIGS. 3 and 4a-d. It shouldbe understood by those skilled in the art that the mode switch of thepresent invention should not be limited to the example illustrated inFIGS. 5a through 5 d. It is anticipated that the mode switch can be madein any number of configurations. The key point of the invention is theselectable I/O path design concept.

FIG. 5a shows the mode switch 500 and mode selector 520 for signalsoriginated from the internal circuits 508 from the first or second orother integrated circuit chips. Alternately, FIG. 5b shows the modeswitch 500 and mode selector 520 for signals originated externally andtransferred to the internal circuits 508 of the first or second or otherintegrated circuit chips.

Referring now to FIG. 5a, the first terminal of the mode switch 500 isconnected to the internal circuits 508, the second terminal of the modeswitch 500 is connected to the I/O or test interface circuit 510 and thethird terminal of the mode switch 500 is connected to the interchipinput/output pad 530. Thus, one of two paths may be selected by the modeswitch. The second terminal of the mode switch connects to the pathincluding a driver circuit 514 and an ESD protection circuit 516 to beused for single chip operation. The third terminal connects to the pathto the chip pad 530 having no extra loading to be used for multi-chipoperation.

The mode switch is comprised of the pass switches 502 and 504 andinverter 506. The pass switch 502 is the parallel combination of then-channel metal oxide semiconductor (NMOS) transistor 502 a andp-channel metal oxide semiconductor (PMOS) transistor 502 b. Likewise,the pass switch 504 is the parallel combination of the NMOS transistor504 a and the PMOS transistor 504 b. The first terminal of the modeswitch 500 and thus the internal circuits 508 are connected to thedrains of the pass switches 502 and 504. The sources of the pass switch502 are connected to the third terminal of the mode switch 500 and thusto the interchip input/output pad 530. The sources of the pass switch504 are connected to the second terminal of the mode switch 500 and thusto the I/O or test interface circuit 510. The gates of the NMOStransistor 504 a and the PMOS transistor 502 b are connected to theoutput of the inverter 506. The gates of the NMOS transistor 502 a, PMOStransistor 504 b, and the input of the inverter 506 are connected to thecontrol terminal of the mode switch 500 and thus to the mode selector520.

An ESD protection circuit 507 is added to prevent damage to the modeswitch during testing and assembly. After the chip is assembled, the ESDprotection circuit will not influence performance of the chip.

When the control terminal of the mode switch 500 is at the first logicstate (0), in this case a voltage level approaching that of thesubstrate biasing voltage source V_(SS), the pass switch 504 is turnedon and the pass switch 502 is turned off. The internal circuits are nowset for single chip operation; for example, the internal circuits may beeffectively connected to the I/O or test interface circuit 510.Conversely, when the control terminal of the mode switch 500 is at thesecond logic state, in this case a voltage level approaching that of thepower supply voltage source V_(DD), the pass switch 502 is turned on andthe pass switch 504 is turned off. This effectively connects theinternal circuits 508 to the interchip input/output pad 530. In thislogic state, the extra electrical load is from the drain of the passswitch 502 and the pass switch 504. This electrical load is very smalland thus highly improved performance can be expected over the prior art.

The I/O or test interface circuit 510 is comprised of the driver circuit514 and the ESD protection circuit 516. The I/O or test interfacecircuit functions as described in FIGS. 4a and 4 c.

The mode select circuit is the interchip input/output pad 522 and theI/O or test input/output pad 524 connected together and to the controlterminal of the mode switch 500. The interchip input/output pad 522 isconnected as described in FIG. 3 to a mating interchip input/output pad562 that are joined by a solder bump or ball. The mating interchipinput/output pad 562 is on the mating chip 560 and is connected to thepower supply voltage source V_(DD) to provide the second logic state tothe control terminal of the mode switch 500 during multi-chip modeoperation. The I/O or test input/output pad is connected to an externalsource 550 during single chip operation. For example, during testing, atest probe or needle 552 is brought in contact with the testinput/output pad. The test probe or needle 552 is connected on a probecard 554 within the test system 550 to the substrate biasing voltagesource V_(ss) to provide the first logic state to the control terminalof the mode switch 500. The external source 550 could also be from asubstrate or a printed circuit board, and so on.

The fundamental connections shown in FIG. 5b are as described in FIG. 5aexcept the I/O signal originates from an external system attached to theinput/output pad 540. The I/O or test interface circuit 510 in this caseis comprised of the receiver 518 and the ESD protection circuit andfunctions as described in FIGS. 4b and 4 d.

Signals originating from the external circuits are applied to theinterchip input/output pad 530 and transferred through the pass switch502 to the internal circuits 508 during multi-chip mode operation.Likewise, the external signals are transferred from the I/O or testinterface 510 through the pass switch 504 to the internal circuits 508during single chip operation.

It is preferred not to have ESD protection on node 3 of the circuitconnected to the input/output pad 530 because ESD loading will impactchip performance after assembly. However, ESD may impact this nodeduring testing and assembly, for example. Therefore, a small ESDprotection circuit 532 may be added on this node, as shown in FIG. 5c(corresponding to FIG. 5a) and FIG. 5d (corresponding to FIG. 5b).

FIG. 6a shows a top surface view of the first integrated circuit chip600 illustrating the placement of the test input/output pads 605 and theinterchip input/output pads 610. The interchip input/output pads 610form an area array of solder balls or bumps 315 of FIG. 3. The I/O ortest input/output pads 605 are peripherally arranged so that the testprobes or needles of the test system can conveniently make contact withthe test input/output pads 605.

FIG. 6b shows the top surface view of the second integrated circuit chip615 illustrating the placement of the interchip input/output pads 625and the external input/output pads 620. The interchip input/output pads625 form the area array to mate with the interchip input/output pads 610of FIG. 5a. The first integrated circuit chip 600 is mounted “face-toface” to the second integrated circuit chip 615. The test input/outputpads 605 must have nothing on the surface of the second integratedcircuit chip 625 in their “shadow.”

The test input/output pads 630 and the external input/output pads 620are formed in the periphery of the second integrated circuit chip 615.The external input/output pads 620 must be placed outside the shadow ofthe first integrated circuit chip 600. The test input/output pads 630are placed conveniently so that test probes or needles of a test systemcan contact the test input/output pads 630. The test input/output pads605 and 630 are connected as shown in FIGS. 5a and 5 b to the I/O ortest interface 510. The test input/output pads 605 and 630 transferstimulus and response signals between the test system 550 and either thefirst integrated circuit chip 600 or second integrated circuit chip 615.

While this invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

The invention claimed is:
 1. A method of forming a multiple integratedcircuit chip structure comprising the steps of: simultaneously butseparately forming internal circuits on a plurality of semiconductorwafers containing a plurality of integrated circuit chips;simultaneously forming input/output circuits on said plurality ofsemiconductor wafers; simultaneously forming interchip interfacecircuits on said plurality of semiconductor wafers, whereby forming saidinterchip interface circuit comprises the steps of: forming an internalinterface circuit for transferring electrical signals between each ofsaid plurality of integrated circuit chips to each other of saidintegrated circuit chips; forming a mode select switch having a firstterminal connected to an output of the internal interface circuit and asecond terminal connected to the internal circuitry of one of saidplurality of integrated circuit chips; forming a mode selector toselectively connect the output of the internal interface circuit to theinternal circuitry of said one of said integrated circuit chips duringmulti-chip operation and the output of the internal interface circuit tothe input/output circuits during single chip operation; during singlechip operation, contacting, stimulating, and examining a response oftest circuits connected to said input/output circuitry and input/outputinterface circuits on the said plurality of wafers; separating saidplurality of semiconductor wafers into a plurality of separatedintegrated circuit chips; contacting with sockets, stimulating andburning-in the plurality of separated integrated circuit chips for anextended period of time; contacting, stimulating, and examining theplurality of separated integrated circuit chips; discarding defectiveintegrated circuit chips; attaching each functioning chip of one of saidsemiconductor wafers to one or more functioning chips of one or more ofother of said plurality of semiconductor wafers; and contacting theinput/output interface circuits, stimulating, and examining the responseof the formed multiple integrated circuit chip structure.
 2. The methodof claim 1 wherein the attaching of each of said integrated circuitchips of one of said semiconductor wafers to said one or more chips ofsaid one or more of said other of said plurality of semiconductor wafersis accomplished by forming an interconnection means between each of theplurality of integrated circuit chips wherein said plurality ofintegrated circuit chips may be attached on one side and/or on oppositesides of said interconnection means.
 3. The method of claim 1 whereinsaid forming said input/output circuits comprises the steps of: formingI/O or test interface circuits connected to external I/O sources; andforming ESD protection circuitry to protect said first and secondintegrated circuit chips from electrostatic discharge voltages.
 4. Themethod of claim 1 wherein contacting said I/O or test interface circuitcomprises temporarily connecting external test circuitry through aninput/output pad to said I/O or test interface circuit.
 5. The method ofclaim 1 wherein said plurality of integrated circuit chips on each ofsaid plurality of semiconductor wafers are fabricated using a differenttypes of semiconductor processes.
 6. The method of claim 1 wherein theinterchip interface circuit is formed with no electrostatic dischargeprotection circuit.
 7. The method of claim 1 wherein the interchipinterface circuit is formed with an electrostatic discharge protectioncircuit.
 8. The method of claim 1 wherein the mode switch comprises: afirst pass switch having a drain terminal connected to the internalcircuits, a source terminal connected to an input/output pad connectedto an attached integrated circuit chip, a first gate terminal connectedto the mode selector, and a second gate terminal; a second pass switchhaving a drain terminal connected to the internal circuits, a sourceterminal connected to the input/output pad connected to the attachedintegrated circuit chip, a first gate terminal, and a second gateterminal connected to the mode selector; an inverter circuit having aninput terminal connected to the mode selector and an output terminalconnected to the second gate terminal of the first pass switch and thefirst gate of the second pass switch; and an electrostatic dischargeprotection circuit.
 9. The method of claim 8 wherein the first andsecond pass switches are comprised of an NMOS transistor and PMOStransistor connected in parallel with a gate of the NMOS transistorbeing the first gate terminal of the first and second pass switches anda gate of the PMOS transistor being the second gate terminal of thefirst and second pass switches.
 10. The method of claim 1 wherein themode switch comprises: a first pass switch having a drain terminalconnected to the internal circuits, a source terminal connected to aninput/output pad connected to an attached integrated circuit chip, afirst gate terminal connected to the mode selector, and a second gateterminal; a second pass switch having a drain terminal connected to theinternal circuits, a source terminal connected to the input/output padconnected to the attached integrated circuit chip, an electrostaticdischarge protection circuit attached to said input/output pad, a firstgate terminal, and a second gate terminal connected to the modeselector; an inverter circuit having an input terminal connected to themode selector and an output terminal connected to the second gateterminal of the first pass switch and the first gate of the second passswitch; and an electrostatic discharge protection circuit.
 11. Themethod of claim 10 wherein the first and second pass switches arecomprised of an NMOS transistor and PMOS transistor connected inparallel with a gate of the NMOS transistor being the first gateterminal of the first and second pass switches and a gate of the PMOStransistor being the second gate terminal of the first and second passswitches.
 12. The method of claim 1 wherein in the mode switchcomprises: an I/O or test input/output pad connected to a first logicstate generator during single chip mode operation; and an interchipinput/output pad connected to a second logic state generator duringmulti-chip mode operation.
 13. The method of claim 1 wherein a modeselect signal is input to said mode selector from one of the following:said first integrated circuit chip, one of said plurality of secondintegrated circuit chips, a test interface, and another external source.